Gal,

There are a variety of inorganic, inert media on the market, and each has
its own properties in relation to moisture-holding capacity, capillarity,
mineral buildup, etc.

Lava rock is known for the mineral buildup problem, but that is affected by
the purity of your water supply, the chemical source of your fertilizers,
it's concentration, how often you flush the pots, etc.

Check out the info on "semi-hydroponics" at the URL below. You may find it
useful.

With any such medium, you're going to have to use a complete nutrient, as
the plant gets essentially nothing from the medium. Personally, I think the
same is mostly true for organic-based media as well, or at the very least,
the nutrition coming from the medium is insufficient.

--

Ray Barkalow First Rays Orchids
http://www.firstrays.com
Secure Online Ordering & Lots of Free Info!


"gal" wrote in message
om...
Hello,

I bought a Dend that is potted in 100% small red porous pebbles, which
I think is volcanic rock. This is the most common potting material for
plants here (Israel) and special orchid potting material is not easy
to find.
All my orchids are potted in a mixture of moss, bark and charcoal but
after having a look at the new Dend and its roots I am thinking about
repotting everything with volcanic rock.

The advantages as I see them a
Good drainage and good air flow through the roots. I was surprise to
see that the rocks do not dry very quickly and I think I will have to
water every five to six day. Future more it is easy to have a look at
the roots by removing the top layer of the rocks.

The disadvantages a
The rocks will accumulate slats and fertilizing material and will have
to be replaced. Since there is no organic matter I am worried that
the plant will get "less value" from the potting material.

I would appreciate your comments.

Regards

Gal